Liquid jetting device

ABSTRACT

A liquid jetting apparatus ( 50 ) to jet a droplet of a charged liquid solution onto a base material, having: a nozzle ( 51 ) in which an edge portion thereof is arranged to face the base material K having a receiving surface to receive the jetted droplet, and an inside diameter of the edge portion from which the droplet is jetted is not more than 30 [μm]; and a liquid solution supplying section ( 35 ) to supply the liquid solution into the nozzle ( 51 ), wherein a jetting electrode ( 58 ) of the jetting voltage applying section ( 35 ) is provided on a back end portion side of the nozzle, and an inside passage length of the nozzle is set to at least not less than ten times of the inside diameter.

CROSS REFERENCE TO RELATED APPLICATION

This is a U.S. national stage of application No. PCT/JP2003/012100,filed on 22 Sep. 2003. Priority under 35 U.S.C. §119(a) and 35 U.S.C.§365(b) is claimed from Japanese Application No. 2002-278232, filed 24Sep. 2002 and Japanese Application No. 2003-293055, filed 13 Aug. 2003,the disclosures of which are also incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a liquid jetting apparatus for jettingliquid to a base material.

BACKGROUND ART

As a conventional inkjet recording method, a piezo method for jetting anink droplet by changing a shape of an ink passage according to vibrationof a piezoelectric element, and a thermal method for making a heatgenerator provided in an ink passage heat to generate air bubbles andjetting an ink droplet according to a pressure change by the air bubblesin the ink passage are known, however, recently, an electrostaticsucking method for charging ink in an ink passage to jet an ink dropletby a electrostatic sucking force of the ink such as one described inJP-Tokukaihei-11-277747 or JP-Tokukai-2000-127410 has been increasing.

However, the above-mentioned inkjet recording method has the followingproblems.

(1) Limit and Stability of a Minute Liquid Droplet Formation

Since a nozzle diameter is large, a shape of a droplet jetted from anozzle is not stabilized, and there is a limit of making a dropletminute.

(2) High Applying Voltage

For jetting a minute droplet, miniaturization of a jet opening of thenozzle is an important factor. In a principle of the conventionalelectrostatic sucking method, since the nozzle diameter is large,electric field intensity of a nozzle edge portion is weak, andtherefore, in order to obtain necessary electric field intensity forjetting a droplet, it is necessary to apply a high jetting voltage (forexample, extremely high voltage near 2000[V]). Accordingly, in order toapply a high voltage, a driving control of a voltage becomes expensive.

Thereupon, to provide a liquid jetting apparatus capable of jetting aminute droplet is a first object. At the same time, to provide a liquidjetting apparatus capable of jetting a stable droplet is a secondobject. Further, to provide a liquid jetting apparatus in which it ispossible to jet a minute droplet and landing accuracy is high is a thirdobject. Further, to provide a liquid jetting apparatus which can reducean applying voltage and is cheap is a fourth object.

DISCLOSURE OF THE INVENTION

The present invention has a structure in which the liquid jettingapparatus to jet a droplet of a charged liquid solution onto a basematerial, comprises:

a liquid jetting head comprising a nozzle to jet the droplet from anedge portion, an inside diameter of the edge portion of the nozzle beingnot more than 30 [μm];

a liquid solution supplying section to supply the liquid solution intothe nozzle; and

a jetting voltage applying section to apply a jetting voltage to theliquid solution in the nozzle,

wherein an inside passage length of the nozzle is set to at least notless than ten times of the inside diameter of the nozzle at the nozzleedge portion.

Hereinafter, the nozzle diameter indicates the inside diameter of thenozzle at the edge portion from which a droplet is jetted (insidediameter at the edge portion of the nozzle). A shape of cross section ofa droplet jetting hole in the nozzle is not limited to a round shape.For example, in the case where the cross-sectional shape of the liquidjetting hole is a polygon shape, a star-like shape or other shape, itindicates that the circumcircle of the cross-sectional shape is not morethan 30 [μm]. Hereinafter, regarding to the nozzle diameter or theinside diameter at the edge portion of the nozzle, it is to be the sameeven when other numerical limitations are given. The nozzle radiusindicates the length of ½ of the nozzle diameter (inside diameter of theedge portion of the nozzle).

In the present invention, “base material” indicates an object to receivelanding of a droplet of the liquid solution jetted, and material thereofis not specifically limited. Accordingly, for example, when applying theabove structure to the ink jet printer, a recording medium such as apaper, a sheet or the like corresponds to the base material, and whenforming a circuit by using a conductive paste, the base on which thecircuit is to be made corresponds to the base material.

In the above structure, the nozzle or the base material is arranged sothat a receiving surface where a droplet lands faces the edge portion ofthe nozzle. The arranging operation to realize the positional relationwith each other may be performed by moving either the nozzle or the basematerial.

Then, the liquid solution is supplied to the inside of the liquidjetting head by the liquid solution supplying section. The liquidsolution in the nozzle needs to be in a state of being charged forperforming jetting. An electrode exclusively for charging may beprovided to apply a voltage needed to charge the liquid solution.

The liquid solution is charged in the nozzle, so that the electric fieldintensity is concentrated. The liquid solution receives an electrostaticforce toward the nozzle edge portion side, so that a state where theliquid solution protrudes at the nozzle edge portion (convex meniscus)is formed. When the electrostatic pressure exceeds a surface tension atthe convex meniscus, a droplet of the liquid solution flies from theprotruding edge portion of the convex meniscus in a directionperpendicular to the receiving surface of the base material, therebyforming a dot of the liquid solution on the receiving surface of thebase material.

In the above structure, attempt is made to super miniaturize the nozzlediameter to obtain the effect of electric field concentration, however,for the liquid solution to obtain further intense electric fieldintensity at the nozzle edge portion, a droplet to be in a charged stateis preferably elongated. Therefore, the inside passage length of thenozzle may be set to long. Based on this view, after considering theresults of a relation between the inside passage length of the nozzleand responsiveness by a comparative study, the result was obtained, inwhich responsiveness is improved when the inside passage length of thenozzle is set to ten times of the inside diameter of the nozzle. Thatis, by setting the inside passage length of the nozzle to not less thanten times of the inside diameter of the nozzle, responsiveness ofjetting at the miniaturized nozzle can be improved.

Preferably, the passage length of the in-nozzle passage is longer,however, it is preferable to choose a value (multiplication factor tothe inside diameter) in consideration of difficulty of manufacturing,decrease of jetting stability by clogging or the like. As one example,the upper limit is set to around 150 times.

Here, the inside passage length of the nozzle indicates a distance Hfrom a nozzle plate surface to the nozzle edge in a case of a liquidjetting head having a nozzle arranged on the nozzle plate (refer to FIG.12).

Further, in the present invention, the electric field intensity becomeshigh by concentrating the electric filed at the nozzle edge portion withthe use of the nozzle having a super minute diameter which cannot befound conventionally, and at that time, an electrostatic force which isgenerated between the distance to an image charge on the base materialside is induced, thereby a droplet flies.

Accordingly, jetting a droplet can be performed with a lower voltagethan that which has been conventionally considered, even with the minutenozzle, and can be favorably performed even when the base material ismade of conductive material or insulating material.

In this case, jetting a droplet can be performed even when there is nocounter electrode facing the edge portion of the nozzle. For example, inthe case that the base material is arranged to face the nozzle edgeportion in the state were there is no counter electrode, when the basematerial is a conductor, an image charge with reversed polarity isinduced at a position which is plane symmetric with the nozzle edgeportion with respect to the receiving surface of the base material as astandard, and when the base material is an insulator, an image chargewith reversed polarity is induced at a symmetric position which isdefined by dielectric constant of the base material with respect to thereceiving surface of the base material as a standard. Flying of adroplet is performed by an electrostatic force between the electriccharge induced at the nozzle edge portion and the image charge.

Thereby, the number of components in the structure of the apparatus canbe reduced. Accordingly, when applying the present invention to abusiness ink jet system, in can contribute to improvement ofproductivity of the whole system, and also the cost can be reduced.

However, although the structure of the present invention can eliminatethe use of a counter electrode, the counter electrode may be used at thesame time. When the counter electrode is used at the same time,preferably, the base material is arranged to be along the facing surfaceof the counter electrode and the facing surface of the counter electrodeis arranged to be perpendicular to a direction of jetting a droplet fromthe nozzle, thereby it becomes possible to use an electrostatic force bythe electric field between the nozzle and the counter electrode forinducing a flying electrode. Moreover, by grounding the counterelectrode, an electric charge of a charged droplet can be released viathe counter electrode in addition to discharging the electric charge tothe air, so that the effect to reduce storage of electric charges canalso be obtained. Thus, using the counter electrode at the same time canbe described as a preferable structure.

In addition to the above structure, the inside passage length of thenozzle may be set to at least not less than 50 times of the insidediameter of the nozzle at the nozzle edge portion.

In this structure, by setting the inside passage length of the nozzle toat least not less than 50 times of the inside diameter, responsivenesscan be improved and the electric field can be concentrated moreeffectively, enabling to jet a more minute droplet.

Moreover, in addition to the above structure, the inside passage lengthof the nozzle may be set to at least not less than 100 times of theinside diameter of the nozzle at the nozzle edge portion.

In this structure, by setting the inside passage length of the nozzle toat least not less than 100 times of the inside diameter, responsivenesscan be improved and a jetted droplet can be minute, and also theelectric field can be concentrated more effectively, thereby enabling tostably concentrate the jetting position.

Moreover, in addition to the above structure, a wall thickness of thenozzle at the edge portion of the nozzle may be set to not more than alength equal to the inside diameter of the nozzle at the nozzle edgeportion.

Thereby, an outside diameter of an edge surface of the nozzle can be setto not more than three times of the inside diameter, so that an area ofthe edge surface can be small, and the size of the edge surface can bedefined with the inside diameter of the nozzle as a standard. Thus, theoutside diameter of the nozzle edge can be defined according to theminiaturization of the inside diameter of the nozzle. As a result, theoutside diameter of the convex meniscus which is formed at the nozzleedge portion and protrudes to a jetting direction can be miniaturizedaccording to the nozzle inside diameter, so that jetting operation by aconcentrated electric field is concentrated to the meniscus edge portionmore effectively. Thus, responsiveness can be improved and a droplet canbe minute.

Moreover, the wall thickness of the nozzle at the edge portion of thenozzle may be set to not more than ¼ of the length equal to the insidediameter of the nozzle at the nozzle edge portion.

Thereby, the outside diameter of the edge surface of the nozzle can beset to not more than 1.5 times of the inside diameter, so that the areaof the edge surface can be smaller, and the size of the edge surface canbe defined with the inside diameter of the nozzle as a standard. Thus,the outside diameter of the nozzle edge can be defined according to theminiaturization of the inside diameter of the nozzle. As a result, theoutside diameter of the convex meniscus which is formed at the nozzleedge portion and protrudes to the jetting direction can be miniaturizedaccording to the nozzle inside diameter, so that jetting operation bythe concentrated electric field is concentrated to the meniscus edgeportion more effectively. Thus, responsiveness can be further improvedand a droplet can be further minute.

Moreover, at least the edge portion of a surface of the nozzle may besubjected to a water repellent processing.

Thereby, the convex meniscus according to the inside diameter of thenozzle can be formed, and the meniscus which is convex toward thejetting side can be formed more stably due to water repellency aroundthe jetting hole at the nozzle edge, so that the jetting operation bythe concentrated electric field is concentrated to the meniscus edgeportion more effectively. Thus, responsiveness can be further improvedand a droplet can be further minute.

Moreover, the edge surface of the nozzle may comprise an inclinedsurface with respect to a centerline of the in-nozzle passage.

Thereby, the liquid solution can be concentrated on a side of thejetting edge portion with a sharp shape formed by the inclined surfaceand the side surface of the nozzle, so that the jetting operation by theconcentrated electric field is concentrated to the meniscus edge portionmore effectively. Thus, responsiveness can be further improved and adroplet can be further minute.

Moreover, in addition to the above structure, an inclination angle ofthe edge surface of the nozzle may be in a range of 30 to 45 degrees.

The above “inclination angle” indicates an angle defined based on astandard in which the state where a normal line of the inclined surfaceaccords to the centerline of the in-nozzle passage is defined as 90degrees.

Considering only to concentrate the liquid solution to the edge portionof the inclined surface, it is preferable that the edge surface is moreinclined to a direction that the edge portion is sharpened, however,when this angle is too small, discharge from the edge portion easilyoccurs, so that adversely, it may undermine the effect of the electricfield concentration. Thus, to avoid such a thing, the inclination angleof the inclined surface is set to be in the range of 30 to 45 degrees,so that responsiveness can be further improved and a droplet can befurther minute without undermining the effect of electric fieldconcentration.

Moreover, in addition to the above described structure, the nozzlediameter may be less than 20 [μm].

Thereby, electric field intensity distribution becomes narrow.Therefore, the electric field can be concentrated. This results inmaking a droplet formed minute and stabilizing the shape thereof, andreducing the total applying voltage. The droplet is accelerated by anelectrostatic force acting between the electric field and the chargejust after jetted from the nozzle. However, the electric field rapidlydecreases as the droplet moves away from the nozzle. Thus, thereafter,the droplet decreases the speed by air resistance. However, the minutedroplet with concentrated electric field is accelerated as it approachesthe counter electrode by an image force. By balancing the decelerationby air resistance and the acceleration by the image force, the minutedroplet can stably fly and landing accuracy can be improved.

Moreover, the inside diameter of the nozzle may be not more than 10[μm].

Thereby, the electric field can further be concentrated, so that adroplet can further be made minute and the effect to the electric fieldintensity distribution by the distance change to the counter electrodewhen flying can be reduced. This results in reducing the effects to thedroplet shape or the landing accuracy by the positional accuracy of thecounter electrode or, the property or the thickness of the basematerial.

Moreover, the inside diameter of the nozzle may be not more than 8 [μm].

Thereby, the electric field can further be concentrated, so that adroplet can further be made minute and the effect to the electric fieldintensity distribution by the distance change to the counter electrodewhen flying can be reduced. This results in reducing the effects to thedroplet shape or the landing accuracy by the positional accuracy of thecounter electrode or, the property or the thickness of the basematerial.

Further, with the degree of the electric field concentration becomeshigh, the effect of electric field crosstalk which is a problem whenarranging nozzles in high density at the time of using a plurality ofnozzles is reduced, enabling to arrange the nozzles with further highdensity.

Moreover, the inside diameter of the nozzle may be not more than 4 [μm].With this structure, the electric field can significantly beconcentrated, making maximum electric field intensity high, and adroplet can be minute with a stable shape and the initial speed of thedroplet can be increased. Thereby, flying stability improves, resultingin further improving the landing accuracy and jetting responsiveness.

Further, with the degree of the electric field concentration becomeshigh, the effect of electric field crosstalk which is a problem whenarranging nozzles with high density at the time of using a plurality ofnozzles is reduced, enabling to arrange the nozzles with further highdensity.

Moreover, the inside diameter of the nozzle is preferably more than 0.2[μm]. By making the inside diameter of the nozzle be more than 0.2 [μm],charging efficiency of a droplet can be improved. Thus, jettingstability can be improved.

Moreover, a jetting electrode of the jetting voltage applying sectionmay be provided on a back end portion side of the nozzle.

Thereby, the jetting electrode is positioned near the upstream edgeportion of the in-nozzle passage, so that the jetting electrode can beapart from the edge portion for jetting the liquid solution. Therefore,the effect of disturbance by the jetting electrode which continuouslyperforms potential changes can be reduced and the liquid solution can bestably jetted.

Further, in each above described structure, preferably the nozzle isformed with an electrical insulating material, and an electrode forapplying a jetting voltage is inserted in the nozzle or a plating tofunction as the electrode is formed.

Further, preferably the nozzle is formed with an electrical insulatingmaterial, an electrode for applying a jetting voltage is inserted in thenozzle or a plating to function as the electrode is formed, and anelectrode for jetting is provided on the outside of the nozzle.

The electrode for jetting outside the nozzle is, for example, providedat the end surface of the edge portion side of the nozzle, or the entirecircumference or a part of the side surface of the edge portion side ofthe nozzle.

Further, in addition to the operational effects by the above describedstructures, a jetting force can be improved. Thus, a droplet can bejetted with low voltage even when further making the nozzle diameterminute.

Further, preferably, the base material is formed with a conductivematerial or an insulating material.

Further, preferably, the jetting voltage to be applied is driven in therange described by the following equation (1).

$\begin{matrix}{{h\sqrt{\frac{\gamma\;\pi}{ɛ_{0}d}}} > V > \sqrt{\frac{\gamma\;{kd}}{2ɛ_{0}}}} & (1)\end{matrix}$where, γ: surface tension of liquid solution [N/m], ∈₀: electricconstant [F/m], d: nozzle diameter [m], h: distance between nozzle andbase material [m], k: proportionality constant dependent on nozzle shape(1.5<k<8.5)

Further, preferably, the jetting voltage to be applied is not more than1000V.

By setting the upper limit of the jetting voltage in this way, jettingcontrol can be made easy, and reliability can be easily improved byperforming improvement of durability of the apparatus and securitymeasures.

Further, preferably, the jetting voltage to be applied is not more than500V.

By setting the upper limit of the jetting voltage in this way, jettingcontrol can be further made easy, and reliability can be furtherimproved easily by performing further improvement of durability of theapparatus and security measures.

Further, preferably, a distance between the nozzle and the base materialis not more than 500 [μm], because high landing accuracy can be obtainedeven when making the nozzle diameter minute.

Further, preferably, the structure is such that a pressure is applied tothe liquid solution in the nozzle.

Further, when jetting is performed at a single pulse, a pulse width Δtnot less than a time constant τ determined by the following equation (2)may be applied.

$\begin{matrix}{\tau = \frac{ɛ}{\sigma}} & (2)\end{matrix}$where, ∈: dielectric constant of liquid solution [F/m], and σ:conductivity of liquid solution [S/m].

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view showing an electric field intensity distribution witha nozzle diameter as ø0.2 [μm] and with a distance from a nozzle to acounter electrode set to 2000 [μm], and FIG. 1B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 2A is a view showing an electric field intensity distribution withthe nozzle diameter as ø0.4 [μm] and with the distance from the nozzleto the counter electrode set to 2000 [μm], FIG. 2B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 3A is a view showing an electric field intensity distribution withthe nozzle diameter as ø1 [μm] and with a distance from the nozzle tothe counter electrode set to 2000 [μm], FIG. 3B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 4A is a view showing an electric field intensity distribution withthe nozzle diameter as ø8 [μm] and with the distance from the nozzle tothe counter electrode set to 2000 [μm], FIG. 4B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 5A is a view showing an electric field intensity distribution withthe nozzle diameter as ø20 [μm] and with the distance from the nozzle tothe counter electrode set to 2000 [μm], FIG. 5B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 6A is a view showing an electric field intensity distribution withthe nozzle diameter as ø50 [μm] and with the distance from the nozzle tothe counter electrode set to 2000 [μm], FIG. 6B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 7 is a chart showing maximum electric field intensity under eachcondition of FIGS. 1 to FIGS. 6;

FIG. 8 is a diagram showing a relation between the nozzle diameter ofthe nozzle, and maximum electric field intensity and an intense electricfield area at a meniscus;

FIG. 9 is a diagram showing a relation among the nozzle diameter of thenozzle, a jetting start voltage at which a droplet jetted at themeniscus starts flying, a voltage value at Rayleigh limit of the initialjetted droplet, and a ratio of the jetting start voltage to the Rayleighlimit voltage;

FIG. 10 is a graph described by a relation between the nozzle diameterand the intense electric field area at the meniscus;

FIG. 11 is a sectional view along the nozzle of the liquid jettingapparatus in the first embodiment;

FIG. 12 is an explanation view describing references showing each sizeat the edge portion of the nozzle;

FIG. 13A is an explanation view showing a water repellent processedstate at the edge portion of the nozzle, and FIG. 13B is an explanationview showing other example of the water repellent processing;

FIG. 14A is an explanation view of a relation between a jettingoperation of liquid solution and a voltage applied to the liquidsolution in a state where the jetting is not performed, and FIG. 14B isan explanation view showing the jetting state;

FIG. 15 is an explanation view of showing an example of other nozzleprovided with an inclined surface at the edge;

FIG. 16A is a partially broken perspective view showing an example of ashape of an in-nozzle passage providing roundness at a liquid solutionroom side, FIG. 16B is a partially broken perspective view showing anexample of a shape of the in-nozzle passage having an inside surfacethereof as a tapered circumferential surface, and FIG. 16C is apartially broken perspective view showing an example of a shape of thein-nozzle passage combining the tapered circumferential surface and alinear passage;

FIG. 17 is a chart showing results of a comparative study performedunder a predetermined condition by changing a size of each part of thenozzle;

FIG. 18 is a chart showing results of a comparative study performedunder a predetermined condition by changing a size of each part of thenozzle;

FIG. 19 is a view for describing a calculation of the electric fieldintensity of the nozzle of the embodiments of the present invention;

FIG. 20 is a side sectional view of the liquid jetting apparatus as oneexample of the present invention; and

FIG. 21 is a view for describing a jetting condition according to arelation of distance-voltage in the liquid jetting apparatus of theembodiments of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A nozzle diameter of a liquid jetting apparatus described in thefollowing each embodiment is preferably not more than 30 [μm], morepreferably less than 20 [μm], even more preferably not more than 10[μm], even more preferably not more than 8 [μm], and even morepreferably not more than 4 [μm]. Also, the nozzle diameter is preferablymore than 0.2 [μm]. Hereinafter, in regard to a relation between thenozzle diameter and an electric field intensity, descriptions will behereafter made with reference to FIG. 1A to FIG. 6B. In correspondencewith FIG. 1A to FIG. 6B, electric field intensity distributions in casesof the nozzle diameters being ø0.2, 0.4, 1, 8 and 20 [μm], and a case ofa conventionally-used nozzle diameter being ø50 [μm] as a reference areshown.

Here, in FIG. 1A to FIG. 6B, a nozzle center position C indicates acenter position of a liquid jetting surface of a liquid jetting hole ata nozzle edge. Further, FIG. 1A, FIG. 2A, FIG. 3A, FIG. 4A, FIG. 5A, andFIG. 6A indicate electric field intensity distributions when thedistance between the nozzle and an counter electrode is set to 2000[μm], and FIG. 1B, FIG. 2B, FIG. 3B, FIG. 4B, FIG. 5B, and FIG. 6Bindicate electric field intensity distributions when the distancebetween the nozzle and the counter electrode is set to 100 [μm]. Here,an applying voltage is set constant to 200 [V] in each condition. Adistribution line in FIG. 1A to FIG. 6B indicates a range of electriccharge intensity from 1×10⁶ [V/m] to 1×10⁷ [V/m].

FIG. 7 shows a chart indicating the maximum electric field intensityunder each condition.

According to FIG. 5A and FIG. 5B, the fact that the electric fieldintensity distribution spreads to a large area if the nozzle diameter isnot less than ø20 [μm], was comprehended. Further, according to thechart of FIG. 7, the fact that the distance between the nozzle and thecounter electrode has an influence on the electric field intensity wascomprehended.

From these things, when the nozzle diameter is not more than ø8 [μm](see FIG. 4A and FIG. 4B), the electric field intensity is concentratedand change of a distance to the counter electrode scarcely has aninfluence on the electric field intensity distribution. Therefore, whenthe nozzle diameter is not more than ø8 [μm], it is possible to performa stable jetting without suffering influence of position accuracy of thecounter electrode, and unevenness of base material property andthickness. Next, a relation between the nozzle diameter of the nozzleand the maximum electric field intensity and an intense electric fieldarea when a liquid level is at the edge position of the nozzle is shownin FIG. 8.

According to the graph shown in FIG. 8, when the nozzle diameter is notmore than ø4 [μm], the fact that the electric field concentration growsextremely large and the maximum electric field intensity is made highwas comprehended. Thereby, since it is possible to make an initialjetting speed of the liquid solution large, flying stability of adroplet is increased and a moving speed of an electric charge at thenozzle edge portion is increased, thereby jetting responsivenessimproves.

Continuously, in regard to maximum electric charge amount chargeable toa jetted droplet, description will be made hereafter. Electric chargeamount chargeable to a droplet is shown as the following equation (3),in consideration of Rayleigh fission (Rayleigh limit) of a droplet.

$\begin{matrix}{q = {8 \times \pi \times \sqrt{ɛ_{0} \times \gamma \times \frac{d_{0}^{3}}{8}}}} & (3)\end{matrix}$where q is electric charge amount [C] giving Rayleigh limit, ∈₀ iselectric constant [F/m], γ is surface tension of the liquid solution[N/m], and d₀ is diameter [m] of the droplet.

The closer to a Rayleigh limit value the electric charge amount qcalculated by the above-mentioned equation (3) is, the stronger anelectrostatic force becomes even with the same electric field intensity,thereby improving jetting stability. However, when it is too close tothe Rayleigh limit value, conversely a dispersion of the liquid solutionoccurs at a liquid jet opening of the nozzle, and there is lack ofjetting stability.

Here, FIG. 9 is a graph showing a relation among the nozzle diameter ofthe nozzle, a jetting start voltage at which a droplet jetted at thenozzle edge portion starts flying, a voltage value at Rayleigh limit ofthe initial jetted droplet, and a ratio of the jetting start voltage tothe Rayleigh limit voltage.

From the graph shown in FIG. 9, within the range of the nozzle diameterfrom ø0.2 [μm] to ø4 [μm], the ratio of the jetting start voltage andthe Rayleigh limit voltage value exceeds 0.6, and a favorable result ofelectric charge efficiency of a droplet is obtained. Thereby, it iscomprehended that it is possible to perform a stable jetting within therange.

For example, in a graph represented by a relation between a nozzlediameter and an intense electric field (not less than 1×10⁶ [V/m]) areaat the nozzle edge portion shown in FIG. 10, the fact that an area ofthe electric field concentration becomes extremely narrow when thenozzle diameter is not more than ø0.2 [μm] is indicated. Thereby, thefact that a jetted droplet is not able to sufficiently receive energyfor acceleration and flying stability is reduced is indicated.Therefore, preferably the nozzle diameter is set to more than ø0.2 [μm].

First Embodiment

(Whole Structure of Liquid Jetting Apparatus)

A liquid jetting apparatus will be described below with reference toFIG. 11 to FIGS. 14. FIG. 11 is a sectional view of the liquid jettingapparatus 50 along a nozzle 51 to be described later.

The liquid jetting apparatus 50 is provided on a nozzle plate 56 d andcomprises the nozzle 51 having a super minute diameter for jetting adroplet of chargeable liquid solution from its edge portion, a counterelectrode 23 which has a facing surface to face the edge portion of thenozzle 51 and supports a base material K receiving a droplet at thefacing surface, a liquid solution supplying section 53 for supplying theliquid solution to a passage 52 in the nozzle 51, a jetting voltageapplying section 35 for applying a jetting voltage to the liquidsolution in the nozzle 51, and a liquid solution sucking section 40 forsucking the liquid solution in the nozzle 51. The above-mentioned nozzle51, a partial structure of the liquid solution supplying section 53 anda partial structure of the jetting voltage applying section 35 areintegrally formed as a liquid jetting head.

In FIG. 11, for the convenience of a description, a state where the edgeportion of the nozzle 51 faces upward and the counter electrode 23 isprovided above the nozzle 51 is illustrated. However, practically, theapparatus is so used that the nozzle 51 faces in a horizontal directionor a lower direction than the horizontal direction, more preferably, thenozzle 51 faces perpendicularly downward.

(Liquid Solution)

As an example of the liquid solution jetted by the above-mentionedliquid jetting apparatus 50, as inorganic liquid, water, COCl₂, HBr,HNO₃, H₃PO₄, H₂SO₄, SOCl₂, SO₂CL₂, FSO₂H and the like can be cited. Asorganic liquid, alcohols such as methanol, n-propanol, isopropanol,n-butanol, 2-methyl-1-propanol, tert-butanol, 4-metyl-2-pentanol, benzylalcohol, α-terpineol, ethylene glycol, glycerin, diethylene glycol,triethylene glycol and the like; phenols such as phenol, o-cresol,m-cresol, p-cresol and the like; ethers such as dioxiane, furfural,ethyleneglycoldimethylether, methylcellosolve, ethylcellosolve,butylcellosolve, ethylcarbitol, buthylcarbito, buthylcarbitolacetate,epichlorohydrin and the like; ketones such as acetone, ethyl methylketone, 2-methyl-4-pentanone, acetophenone and the like; aliphatic acidssuch as formic acid, acetic acid, dichloroacetate, trichloroacetate andthe like; esters such as methyl formate, ethyl formate, methyl acetate,ethyl acetate, n-butyl acetate, isobutyl acetate, 3-methoxybutylacetate, n-pentyl acetate, ethyl propionate, ethyl lactate, methylbenzonate, diethyl malonate, dimethyl phthalate, diethyl phthalate,diethyl carbonate, ethylene carbonate, propylene carbonate, cellosolveacetate, butylcarbitol acetate, ethyl acetoacetate, methyl cyanoacetate,ethyl cyanoacetate and the like; nitrogen-containing compounds such asnitromethane, nitrobenzene, acetonitrile, propionitrile, succinonitrile,valeronitrile, benzonitrile, ethyl amine, diethyl amine,ethylenediamine, aniline, N-methylaniline, N,N-dimethylaniline,o-toluidine, p-toluidine, piperidine, pyridine, α-picoline,2,6-lutidine, quinoline, propylene diamine, formamide,N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide,acetamide, N-methylacetamide, N-methylpropionamide,N,N,N′,N′-tetramethylurea, N-methylpyrrolidone and the like;sulfur-containing compounds such as dimethyl sulfoxide, sulfolane andthe like; hydro carbons such as benzene, p-cymene, naphthalene,cyclohexylbenzene, cyclohexyene and the like; halogenated hydrocarbonssuch as 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane,1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane,1,2-dichloroethylene(cis-), tetrachloroethylene, 2-chlorobutan,1-chloro-2-methylpropane, 2-chloro-2-methylpropane, bromomethane,tribromomethane, 1-promopropane and the like can be cited. Further, twoor more types of each of the mentioned liquids may be mixed to be usedas the liquid solution.

Further, conductive paste which includes large portion of materialhaving high electric conductivity (silver pigment or the like) is used,and in the case of performing the jetting, as objective material forbeing dissolved into or dispersed into the above-mentioned liquid,excluding coarse particles causing clogging to the nozzles, it is not inparticular limited. As fluorescent material such as PDP, CRT, FED or thelike, what is conventionally known can be used without any specificlimitation. For example, as red fluorescent material, (Y,Gd)BO₃:Eu,YO₃:Eu and the like, as red fluorescent material, Zn₂SiO₄:Mn,BaAl₁₂O₁₉:Mn, (Ba,Sr,Mg)O.α-Al₂O₃:Mn and the like, blue fluorescentmaterial, BaMgAl₁₄O₂₃:Eu, BaMgAl₁₀O₁₇:Eu and the like can be cited. Inorder to make the above-mentioned objective material adhere on arecording medium firmly, it is preferably to add various types ofbinders. As a binder to be used, for example, cellulose and itsderivative such as ethyl cellulose, methyl cellulose, nitrocellulose,cellulose acetate, hydroxyethyl cellulose and the like; alkyd resin;(metha)acrylate resin and its metal salt such as polymethacrytacrylate,polymethylmethacrylate, 2-ethylhexylmethacrylate•methacrylic acidcopolymer, lauryl methacrylate•2-hydroxyethylmethacrylate copolymer andthe like; poly(metha)acrylamide resin such aspoly-N-isopropylacrylamide, poly-N,N-dimethylacrylamide and the like;styrene resins such as polystyrene, acrylonitrile•styrene copolymer,styrene•maleate copolymer, styrene•isoprene copolymer and the like;various saturated or unsaturated polyester resins; polyolefin resinssuch as polypropylene and the like; halogenated polymers such aspolyvinyl chloride, polyvinylidene chloride and the like; vinyl resinssuch as poly vinyl acetate, chloroethene•polyvinyl acetate copolymer andthe like; polycarbonate resin; epoxy resins; polyurethane resins;polyacetal resins such as polyvinyl formal, polyvinyl butyral, polyvinylacetal and the like; polyethylene resins such as ethylene•vinyl acetatecopolymer, ethylene•ethyl acrylate copolymer resin and the like; amideresins such as benzoguanamine and the like; urea resin; melamine resin;polyvinyl alcohol resin and its anion cation degeneration; polyvinylpyrrolidone and its copolymer; alkylene oxide homopolymer, copolymer andcross-linkage such as polyethelene oxide, polyethelene oxide carboxylateand the like; polyalkylene glycol such as polyethylene glycol,polypropylene glycol and the like; poryether polyol; SBR, NBR latex;dextrin; sodium alginate; natural or semisynthetic resins such asgelatin and its derivative, casein, Hibiscus manihot, gum traganth,pullulan, gum arabic, locust bean gum, guar gum, pectin, carrageenan,glue, albumin, various types of starches, corn starch, arum root,funori, agar, soybean protein and the like; terpene resin; ketone resin;rosin and rosin ester; polyvinylmethylether, polyethyleneimine,polystyrene sulfonate, polyvinyl sulfonate and the like can be used.These resins may not only be used as homopolymer but be blended within amutually soluble range to be used.

(Nozzle)

The above nozzle 51 is integrally formed with a nozzle plate 56 c to bedescribed later, and is provided to stand up perpendicularly withrespect to a flat plate surface of the nozzle plate 56 c. Further, atthe time of jetting a droplet, the nozzle 51 is used to perpendicularlyface a receiving surface (surface where the droplet lands) of the basematerial K. Further, in the nozzle 51, the in-nozzle passage 52penetrating from its edge portion along the nozzle center is formed.

The nozzle 51 will be described in more detail referring to FIG. 12 toFIGS. 13. FIG. 12 is an explanation view describing references showingeach size at the edge portion of the nozzle 51, FIG. 13A is anexplanation view showing a water repellent processed state at the edgeportion of the nozzle 51, and FIG. 13B is an explanation view showingother example of the water repellent processing.

In the nozzle 51, an opening diameter of its edge portion and thein-nozzle passage 52 are uniform. As mentioned, these are formed as asuper minute diameter, and are preferably not more than 30 [μm], morepreferably less than 20 [μm], even more preferably not more than 10[μm], even more preferably not more than 8 [μm], and even morepreferably not more than 4 [μm]. As one concrete example of dimensionsof each part, an inside diameter D_(I) of the in-nozzle passage 52 alongthe entire length from the edge portion of the nozzle is set to 1 [μm]to perform concentration of the electric field due to the superminiaturized nozzle. An outside diameter D₀ of the nozzle at the nozzleedge portion is set to 2 [μm], a wall thickness t of the tube at theedge portion of the nozzle 51 is set to 0.5 [μm] which is smaller thanthe length equal to the inside diameter D_(I) to miniaturize the edgesurface of the nozzle 51, thereby miniaturizing the outer diameter ofthe convex meniscus of the liquid solution formed at the edge portion.For further miniaturizing the edge surface of the nozzle 51, the value tmay be set to not more than ¼ of the inside diameter D_(I) (for example,0.2 [μm]).

A diameter D_(max) of the root of the nozzle 51 is 5 [μm], and acircumferential surface of the nozzle is formed to be a taper.

The nozzle diameter is preferably more than 0.2 [μm]. The height of thenozzle 21 may be 0 [μm].

Further, the height of the nozzle 51 (protruding height from the planeof the jetting side of an upper surface layer 56 c to be describedlater) is set to 100 [μm], and is formed as a conic trapezoid shapebeing boundlessly close to a conic shape. Since the in-nozzle passage 52is provided to penetrate through the nozzle 51 and the flat portion ofthe nozzle plate 56 c positioned thereunder, the passage length of thein-nozzle passage 52 becomes not less than 100 [μm] by setting theheight of the nozzle 51 to the above value. In this way, by setting thepassage length of the in-nozzle passage 52 to not less than ten times,preferably 50 times, and more preferably 100 times of the insidediameter of the nozzle at the nozzle edge portion, a jetting forcereceived from the concentrated electric field can be concentrated moreeffectively at the edge portion of the nozzle 51.

The entire nozzle 51 as well as the nozzle plate 56 c is made of glassas insulating material, and is formed by femtosecond laser to be theshape and the size in the drawing.

As shown in FIG. 13A, a water repellent coating 51 a is formed on theedge surface excluding the passage 52 of the nozzle 51. The waterrepellent coating 51 a is formed by, for example, amorphous carbondeposition. Also, the water repellent coating 51 a may be, as shown inFIG. 13B, formed not only on the edge portion of the nozzle 51 but onthe entire surface of the nozzle 51.

A shape of the in-nozzle passage 52 may not be formed linearly with theinside diameter constant as shown in FIG. 11. For example, as shown inFIG. 16A, it may be so formed as to give roundness to a cross-sectionshape at the edge portion of the side of a liquid solution room 54 to bedescribed later, of the in-nozzle passage 52. Further, as shown in FIG.16B, an inside diameter at the end portion of the side of the liquidsolution room 54 to be described later, of the in-nozzle passage 52 maybe set to be larger than an inside diameter of the end portion of thejetting side, and an inside surface at the in-nozzle passage 52 may beformed in a tapered circumferential surface shape. Further, as shown inFIG. 16C, only the end portion at the side of the liquid solution room54 to be describe later, of the in-nozzle passage 52 may be formed in atapered circumferential surface shape and the jetting end portion sidewith respect to the tapered circumferential surface may be formedlinearly with the inside diameter constant.

(Liquid Solution Supplying Section)

The liquid solution supplying section 53 is provided at a position beinginside of the liquid jetting head 26 and at the root of the nozzle 51,and comprises the liquid solution room 54 communicated to the in-nozzlepassage 52, and a supplying passage 57 for guiding the liquid solutionfrom an external liquid solution tank which is not shown, to the liquidsolution room 54.

The above-mentioned liquid solution tank is arranged at the positionhigher than the nozzle plate 56 for supplying the liquid solution to theliquid solution room 54 with moderate pressure by its own weight.

As described above, supplying the liquid solution may be performed byutilizing a pressure difference according to arrangement positions ofthe liquid jetting head 56 and the supplying tank, however, a supplyingpump may be used for supplying the liquid solution. In this case, thesupplying pump supplies the liquid solution to the edge portion of thenozzle 51, and performs supplying the liquid solution while maintainingthe supplying pressure in the range where leakage from the edge portiondoes not occur. Although it depends upon the design of the pump system,basically, the supplying pump operates when supplying the liquidsolution to the liquid jetting head 56 at the start time, jetting theliquid from the liquid jetting head 56, and supplying of the liquidsolution according thereto is performed while optimizing capacity changein the liquid jetting head 56 by a capillary and the convex meniscusforming section and each pressure of the supplying pumps.

(Jetting Voltage Applying Section)

The jetting voltage applying section 35 comprises a jetting electrode 58for applying the jetting voltage at the back end side of the nozzle 51in the nozzle plate 56, that is at a border position between the liquidsolution room 54 and the in-nozzle passage 52, a bias current powersource 30 for always applying a direct current bias voltage to thisjetting electrode 58 and a jetting voltage power source 31 for applyingthe jetting pulse voltage to the jetting electrode 58 with the biasvoltage superimposed to be an electric potential for jetting.

The above-mentioned jetting electrode 58 is directly contacted to theliquid solution in the liquid solution room 54, for charging the liquidsolution and applying the jetting voltage.

The jetting electrode 58 is arranged on the back end portion (endportion opposite to the edge portion) side of the nozzle 51 of thenozzle plate surface to be apart from the edge portion as much aspossible, so that the effect by rapid voltage change of the jettingpulse voltage to be applied or the like to the nozzle edge portion canbe reduced.

In regard to a bias voltage by the bias power source 30, by applying avoltage always within a range within which jetting of the liquidsolution is not performed, width of a voltage applied at the time ofjetting is preliminarily reduced, and thereby responsiveness at the timeof jetting is improved.

The jetting voltage power source 31 outputs a pulse voltage only whenjetting of the liquid solution is performed, and applies to the jettingelectrode 58 by superimposing to the bias voltage which is output to bealways constant. A value of the pulse voltage is set so that thesuperimposed voltage V at this time satisfies a condition of thefollowing equation (1).

$\begin{matrix}{{h\sqrt{\frac{\gamma\;\pi}{ɛ_{0}d}}} > V > \sqrt{\frac{\gamma\;{kd}}{2ɛ_{0}}}} & (1)\end{matrix}$where, γ: surface tension of liquid solution [N/m], ∈₀: electricconstant [F/m], d: nozzle diameter [m], h: distance between nozzle andbase material [m], k: proportionality constant dependent on nozzle shape(1.5<k<8.5).

As one example, the bias voltage is applied at DC300 [V], and the pulsevoltage is applied at 100 [V]. Therefore, the superimposed voltage atjetting is 400 [V].

(Liquid Jetting Head)

The liquid jetting head 56 comprises a base layer 56 a placed at thelowest layer in FIG. 11, a passage layer 56 b which is placed on topthereof and forms a supplying passage of the liquid solution, and thenozzle plate 56 c formed further on top of this passage layer 56 b. Theabove-mentioned jetting electrode 58 is inserted between the passagelayer 56 b and the nozzle plate 56 c.

The above-mentioned base layer 56 a is formed from silicon base plate,highly-insulating resin or ceramic, and a photoresist layer is formed ontop thereof and it is eliminated except for a part corresponding to thesupplying path 57 and the liquid solution room 54 by the insulatingresin layer by developing, exposing and dissolving a pattern of thesupplying path 57 and the liquid solution room 54, and the insulatingresin layer is formed at the eliminated part. This insulating resinlayer functions as the passage layer 56 b. Then, the jetting electrode58 is formed on an upper surface of this insulating resin layer withplating of a conductive element (for example NiP), and further on topthereof, the nozzle plate 56 c made of glass material processed byfemtosecond laser as described above is formed.

Then, the soluble resin layer corresponding to the pattern of thesupplying passage 57 and the liquid solution room 54 is eliminated, andthese supplying passage 57 and the liquid solution room 54 arecommunicated. Finally, deposition of amorphous carbon is performed atthe edge portion of the nozzle 51 to form the water repellent coating 51a, thereby the production of the nozzle plate 56 c is completed.

Material of the nozzle plate 56 c and the nozzle 51 may be, concretely,semiconductor such as Si or the like, conductive material such as Ni,SUS or the like, other than insulating material such as epoxy, PMMA,phenol, soda glass. However, in a case of forming the nozzle plate 56 cand the nozzle 51 from conductive material, at least at the edge portionedge surface of the edge portion of the nozzle 51, more preferably atthe circumferential surface of the edge portion, coating by insulatingmaterial is preferably provided. This is because, by forming the nozzle51 from insulating material or forming the insulating material coatingat its edge portion surface, at the time of applying the jetting voltageto the liquid solution, it is possible to effectively suppress leakageof electric current from the nozzle edge portion to the counterelectrode 53.

(Counter Electrode)

The counter electrode 23 comprises a facing surface perpendicular to aprotruding direction of the nozzle 51, and supports the base material Kalong the facing surface. A distance from the edge portion of the nozzle51 to the facing surface of the counter electrode 23 is, as one example,set to 100 [μm].

Further, since this counter electrode 23 is grounded, the counterelectrode 23 always maintains grounded potential. Therefore, a dropletjetted by an electrostatic force by electric field generated between theedge portion of the nozzle 51 and the facing surface is guided to a sideof the counter electrode 23 at the time of applying the pulse voltage.

Since the liquid jetting apparatus 50 jets a droplet by enhancing theelectric field intensity by the electric field concentration at the edgeportion of the nozzle 51 according to super-miniaturization of thenozzle 51, it is possible to jet the droplet without the guiding by thecounter electrode 23. However, the guiding by an electrostatic forcebetween the nozzle 51 and the counter electrode 23 is preferablyperformed. Further, it is possible to let out the electric charge of acharged droplet by grounding the counter electrode 23.

(Jetting Operation of Minute Droplet by Liquid Jetting)

An operation of the liquid jetting apparatus 50 will be described withreference to FIG. 14A to FIG. 14B. FIG. 14A and FIG. 14B are explanationviews of a relation with a voltage applied to the liquid solution,wherein FIG. 14A shows a state where the jetting is not performed, andFIG. 14B shows the jetting state.

The state is such that the liquid solution has already been supplied tothe in-nozzle passage 52, and in this state, the bias voltage is appliedto the liquid solution via the jetting electrode 58 by the bias powersource 30. In this state, the liquid solution is charged, and meniscuswhich dents in a reentrant form at the liquid solution is formed at theedge portion of the nozzle 51 (FIG. 14A).

When the jetting pulse voltage is applied by the jetting voltage powersource 31, the liquid solution is guided to the edge portion side of thenozzle 51 by an electrostatic force by electric field intensity of theconcentrated electric field at the edge portion of the nozzle 51, theconvex meniscus protruding outward is formed, and the electric field isconcentrated at a top of the convex meniscus, and after all, a minutedroplet is jetted to the counter electrode side against a surfacetension of the liquid solution (refer to FIG. 14B).

Since the above-mentioned liquid jetting apparatus 50 jets a droplet bythe nozzle 51 having minute diameter which cannot be foundconventionally, the electric field is concentrated by the liquidsolution in a charged state in the in-nozzle passage 52, and thereby theelectric field intensity is enhanced. Therefore, jetting of the liquidsolution by a nozzle having a minute diameter (for example, an insidediameter of 100 [μm], which was conventionally regarded as substantiallyimpossible since a voltage necessary for jetting would become too highwith a nozzle having a structure in which concentration of the electricfield is not performed, is now possible with a lower voltage than theconventional one.

Then, since it is a minute diameter, it is possible to do the control toeasily reduce jetting quantity per unit time due to low nozzleconductance, and the jetting of the liquid solution with asufficiently-small droplet diameter (0.8 [μm] according to eachabove-mentioned condition) without narrowing a pulse width is realized.

Further, since the jetted droplet is charged, even though it is a minutedroplet, a vapor pressure is reduced and evaporation is suppressed, andthereby the loss of mass of the droplet is reduced. Thus, the flyingstabilization is achieved and the decrease of landing accuracy of thedroplet is prevented.

Moreover, in the liquid jetting apparatus 50, the length of thein-nozzle passage is set to not less than 100 times of the insidediameter, so that the electric field can be concentrated moreeffectively, thereby responsiveness to the jetting of a droplet can beimproved and a jetted droplet can be minute, and also the jettingposition can be concentrated more stably.

Moreover, a wall thickness of the tube at the edge portion of the nozzle51 is set to not more than the length equal to the inside diameterD_(I), so that the outside diameter of the edge surface of the nozzle 51can be not more than three times of the inside diameter. Thus,concentration of the jetting operation by the concentrated electricfield can be effectively achieved at the meniscus edge portion by makingthe convex meniscus minute, thereby responsiveness can be improved and adroplet can be minute.

Further, since the water repellent coating 51 a is formed on the edgesurface of the surface of the nozzle 51, the convex meniscuscorresponding to the inside diameter of the nozzle 51 can be formed.Thus, concentration of the jetting operation by the concentratedelectric field can be achieved more effectively at the meniscus edgeportion, thereby responsiveness can be improved and a droplet can beminute. In this case, the meaning of making the convex meniscus minuteby thinning the wall thickness t of the nozzle 51 has smallsignificance. However, even in this case, if the liquid solution spreadson the water repellent coating 51 a, the spread can be within the rangeof the edge surface, thereby having an effect to maintain making theconvex meniscus small in two steps.

(Other Nozzle)

Regarding to the edge shape of the nozzle 51, as shown in FIG. 15, theedge surface of the nozzle 51 may be an inclined surface 51 b withrespect to a centerline of the in-nozzle passage 52. An inclinationangle θ of the edge surface 51 b (the state where a normal line of theinclined surface 51 b accords to the centerline of the in-nozzle passageis defined as 90 degrees) is preferably in a range of 30-45 [°], andhere, it is set to 40 [°]. By making the edge surface of the nozzle 51be the inclined surface 51 b within the angle range as above, the liquidsolution can be concentrated to the jetting edge portion side by theinclined surface 51 b without undermining the effect of the electricfield concentration by discharge. Thus, concentration of the jettingoperation by the concentrated electric field can be achieved moreeffectively at the meniscus edge portion, thereby responsiveness can beimproved and a droplet can be minute.

(Others)

For obtaining electro wetting effect to the nozzle 51, an electrode maybe provided at a circumference of the nozzle 51, or an electrode may beprovided at an inside surface of the in-nozzle passage 52 and aninsulating film may cover over it. Then, by applying a voltage to thiselectrode, it is possible to enhance wettability of the inside surfaceof the in-nozzle passage 52 with respect to the liquid solution to whichthe voltage is applied by the jetting electrode 58 according to theelectro wetting effect, and thereby it is possible to smoothly supplythe liquid solution to the in-nozzle passage 52, resulting in preferablyperforming the jetting and improving responsiveness of the jetting.

[Comparative Study 1 of Nozzle]

The results of the comparative study which is performed with a liquidjetting apparatus approximately same as the above described liquidjetting apparatus 50 under the predetermined conditions by changing asize of each part of the nozzle will be explained below. FIG. 17 is achart showing results of the comparative study. The comparative studywas performed for eight kinds of subjects processed from glass materialby femtosecond laser to make each value of D_(I), D₀, D_(max) and H,(refer to FIG. 12) at the upper surface (including the nozzle) of thenozzle plate be the following size.

-   No. 1

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=1 [μm]

-   No. 2

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=9 [μm]

-   No. 3

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=10 [μm]

-   No. 4

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=49 [μm]

-   No. 5

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=50 [μm]

-   No. 6

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=51 [μm]

-   No. 7

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=99 [μm]

-   No. 8

D_(I)=1 [μm], D₀=2 [μm], D_(max)=5 [μm], H=100 [μm]

The structure other than the above described conditions is same as theliquid jetting apparatus 50 shown in the first embodiment. That is, thenozzle with the inside diameter of the in-nozzle passage and the jettingopening of 1 [μm] is used.

Further, as the driving conditions, (1) a jetted droplet is sampled 100times with frequency of the pulse voltage as a trigger for jetting of 1[kHz], (2) the jetting voltage: the bias voltage is 300 [V] and thejetting pulse voltage is 100 [V], (3) distance from the nozzle edge tothe counter electrode is 100 [μm], (4) the liquid solution is water,properties thereof are such that a viscosity: 8 [cP](8×10⁻² [Pa/S]), aresistivity: 10⁸ [Ωcm] and a surface tension: 30×10⁻³ [N/m], and (5) thebase member is a glass plate.

Images are taken by a stereoscopic microscope and a digital camera underthe above conditions, and minuteness and evenness are evaluated. Theevaluation is performed on five scales, wherein five shows the bestevenness.

According to the results, when the nozzle height H is 10 [μm] which isten times of the inside diameter, a jetted droplet diameter was mademinute to 1 [μm] equal to the nozzle inside diameter, and evenness wasobserved to be improved three scales.

Further, when the nozzle height H is 50 [μm] which is 50 times of theinside diameter, a jetted droplet diameter was made minute to 0.8 [μm]which is smaller than the nozzle inside diameter, and evenness wasimproved to four and remarkable reduction of unevenness was observed.

Further, when the nozzle height H is 100 [μm] which is 100 times of theinside diameter, evenness was improved to five and remarkable reductionof unevenness of dot diameter was observed.

[Comparative Study 2 of Nozzle]

The results of the comparative study which is performed with a liquidjetting apparatus approximately same as the above described liquidjetting apparatus 50 under the predetermined driving conditions bychanging design condition of each part of the nozzle will be explainedbelow. FIG. 18 is a chart showing results of a comparative study. Thecomparative study was performed for nine kinds of subjects. They areprocessed from glass material by femtosecond laser to make each value ofD_(I), t (refer to FIGS. 12) at the upper surface (including the nozzle)of the nozzle plate be the following size and make the inclination angleof the inclined surface of the nozzle edge be the angle shown below, andeach of the subjects is formed to be one in which the water repellentcoating is not formed, one in which the water repellent coating isformed as shown in FIG. 13A or one in which the water repellent coatingis formed as shown in FIG. 13B

-   No. 1

D_(I)=1 [μm], t=2 [μm], H=10 [μm], water repellent coating: unavailable,inclination angle 90 [°] (no inclination)

-   No. 2

D_(I)=1 [μm], t=1 [μm], H=10 [μm], water repellent coating: unavailable,inclination angle 90 [°] (no inclination)

-   No. 3

D_(I)=1 [μm], t=0.2 [μm], H=10 [μm], water repellent coating:unavailable, inclination angle 90 [°] (no inclination)

-   No. 4

D_(I)=1 [μm], t=1 [μm], H=10 [μm], water repellent coating: only on edgesurface (FIG. 13A), inclination angle 90 [°] (no inclination)

-   No. 5

D_(I)=1 [μm], t=0.2 [μm], H=10 [μm], water repellent coating: edgesurface+circumferential surface (FIG. 13B), inclination angle 90 [°] (noinclination)

-   No. 6

D_(I)=1 [μm], t=2 [μm], H=10 [μm], water repellent coating: edgesurface+circumferential surface (FIG. 13B), inclination angle 90 [°] (noinclination)

-   No. 7

D_(I)=1 [μm], t=1 [μm], H=10 [μm], water repellent coating: edgesurface+circumferential surface (FIG. 13B), inclination angle 40 [°]

-   No. 8

D_(I)=1 [μm], t=0.2 [μm], H=10 [μm], water repellent coating: edgesurface+circumferential surface (FIG. 13B), inclination angle 40 [°] (noinclination)

-   No. 9

D_(I)=1 [μm], t=0.2 [μm], H=10 [μm], water repellent coating: edgesurface+circumferential surface (FIG. 13B), inclination angle 20 [°] (noinclination)

The structure other than the above described conditions is same as theliquid jetting apparatus 50 shown in the first embodiment. That is, thenozzle with the inside diameter of the in-nozzle passage and the jettingopening of 1 [μm] is used.

Further, as the driving conditions, (1) a jetted droplet is sampled 100times with frequency of the pulse voltage as a trigger for jetting of 1[kHz], (2) the jetting voltage: the bias voltage is 300 [V] and thejetting pulse voltage is 100 [V], (3) distance from the nozzle edge tothe counter electrode is 100 [μm], (4) the liquid solution is water,properties thereof are such that a viscosity: 8 [cP](8×10⁻² [Pa/S]), aresistivity: 10⁸ [Ωcm] and a surface tension: 30×10⁻³ [N/m], and (5) thebase member is a glass plate.

Images are taken by a stereoscopic microscope and a digital camera underthe above conditions, and minuteness and evenness are evaluated. Theevaluation is performed on five scales with responsiveness evaluationone as a standard, wherein five shows the best responsiveness.

According to the results, compared to the No. 1 in which the wallthickness t of the nozzle edge portion is 2 [μm] which is larger thanthe inside diameter, when the wall thickness t of the nozzle edgeportion is set to 1 [μm] which is equal to the inside diameter (No. 2),significantly improved responsiveness was observed. When the wallthickness t of the nozzle edge portion is set to 0.2 [μm] (No. 3) whichis smaller than ¼ of the inside diameter, further improvedresponsiveness was observed.

Moreover, compared to the No. 2 in which the water repellent coating isnot provided, when the water repellent coating is provided only on thenozzle edge surface (No. 4), improved responsiveness was observed.

Further, compared to the No. 3 in which the water repellent coating isnot provided, when the water repellent coating is provided on the nozzleedge surface and the circumferential surface (No. 5), significantlyimproved responsiveness was observed.

Moreover, compared to the No. 5 in which the inclination angle of theinclined surface at the nozzle edge surface is 90 [°] (no inclination),when the inclination angle of the inclined surface at the nozzle edgesurface is 40 [°] (No. 8), the most favorable and remarkably improvedresponsiveness was observed.

On the other hand, compared to the No. 5 in which the inclined surfaceis not provided, when the inclination angle of the inclined surface atthe nozzle edge surface is 20 [°] (No. 9), decrease of responsivenesswas observed. This is because the smaller the inclination angle is (theedge has more acute angle), discharge tends to occur easily, so that itis considered that this effect occurred.

[Theoretical Description of Liquid Jetting by Liquid Jetting Apparatus]

Hereinafter, a theoretical description of liquid jetting of the presentinvention and a description of a basic example based on this will bemade. In addition, all the contents such as a nozzle structure, materialof each part and properties of jetted liquid, a structure added aroundthe nozzle, a control condition regarding a jetting operation and thelike in the theory and the basic example described hereafter may be,needless to say, applied in each of the above-mentioned embodiments asmuch as possible.

(Approach to Realize Applying Voltage Decrease and Stable Jetting ofMinute Droplet Amount)

Previously, jetting of a droplet with exceeding a range determined bythe following conditional equation was considered impossible.

$\begin{matrix}{d < \frac{\lambda_{c}}{2}} & (4)\end{matrix}$where, λ_(c) is growth wavelength [m] at liquid level of the liquidsolution for making it possible to jet a droplet from the nozzle edgeportion by an electrostatic sucking force, and it can be calculated byλ_(c)=2πγh ²/∈₀ V ².

$\begin{matrix}{d < \frac{\pi\;\gamma\; h^{2}}{ɛ_{0}V^{2}}} & (5)\end{matrix}$

$\begin{matrix}{V < {h\sqrt{\frac{\pi\;\gamma}{ɛ_{0}d}}}} & (6)\end{matrix}$

In the present invention, a role in an electrostatic sucking type inkjetmethod played by the nozzle is reconsidered, in an area where attemptwas not made since it was conventionally regarded as impossible to jet,it is possible to form a minute droplet by using a Maxwell force or thelike.

An equation for approximately expressing a jetting condition or the likefor the approach to reduce a driving voltage and to realize jetting ofminute droplet amount in this way is derived and therefore describedhereafter.

Descriptions hereafter can be applied to the liquid jetting apparatusdescribed in each of the above-mentioned embodiments of the presentinvention.

Assuming that conductive liquid solution is filled to a nozzle of aninside diameter d and the nozzle is perpendicularly placed with a heighth with respect to an infinite plane conductor as a base material at thismoment. This state is shown in FIG. 19. At this time, it is assumed thatelectric charge induced at the nozzle edge portion is concentrated to ahemisphere portion of the nozzle edge, and is approximately expressed inthe following equation.Q=2π∈₀ αVd  (7)where, Q: electric charge induced at the nozzle edge portion [C], ∈₀:electric constant [F/m], h: distance between nozzle and base material[m], d: diameter of inside of the nozzle [m], and V: total voltageapplied to the nozzle [V]. α: proportionality constant dependent on anozzle shape or the like, taking around 1 to 1.5, especially takesapproximately 1 when d<<h.

Further, when the base plate as the base material is a conductive baseplate, it is considered that an image charge Q′ having opposite sign isinduced to the symmetrical position in the base plate. When the baseplate is insulating material, similarly an image charge Q′ of oppositesign is induced to the symmetrical position determined by aconductivity.

By the way, electric field intensity E_(loc) [V/m] of the edge portionof convex meniscus at the nozzle edge portion is, when a curvatureradius of the convex meniscus is assumed to be R [m], given as

$\begin{matrix}{E_{loc} = \frac{V}{kR}} & (8)\end{matrix}$where, k: proportionality constant, though being different depending ona nozzle shape or the like, taking around 1.5 to 8.5, and in most casesconsidered approximately 5 (P. J. Birdseye and D. A. Smith, SurfaceScience, 23 (1970) 198-210).

Now, for ease, we assume d/2=R. This corresponds to a state where theconductive liquid solution rises in a hemisphere shape having the sameradius as the nozzle radius according to a surface tension force.

We consider a balance of pressure affecting liquid of the nozzle edge.First, when a liquid area at the nozzle edge portion is assumed to be S[m²], electrostatic pressure is given as

$\begin{matrix}{P_{e} = {{\frac{Q}{S}E_{loc}} \approx {\frac{Q}{\pi\;{d^{2}/2}}E_{loc}}}} & (9)\end{matrix}$From the equations (7), (8) and (9), it is assumed that α=1,

$\begin{matrix}{P_{e} = {{\frac{2ɛ_{0}V}{d/2} \cdot \frac{V}{k \cdot {d/2}}} = \frac{8ɛ_{0}V^{2}}{k \cdot d^{2}}}} & (10)\end{matrix}$

Meanwhile, when a surface tension of the liquid at the nozzle edgeportion is P_(s),

$\begin{matrix}{P_{s} = \frac{4\gamma}{d}} & (11)\end{matrix}$where, λ: surface tension [N/m].A condition under which jetting of fluid occurs is, since it is acondition where the electrostatic pressure exceeds the surface tension,given asP_(e)>P_(s)  (12)By using a sufficiently-small nozzle diameter d, it is possible to makethe electrostatic pressure exceed the surface tension.According to this relational equation, when a relation between V and dis calculated,

$\begin{matrix}{V > \sqrt{\frac{\gamma\;{kd}}{2ɛ_{0}}}} & (13)\end{matrix}$gives the minimum voltage of jetting. In other words, from the equation(6) and the equation (13),

$\begin{matrix}{{h\sqrt{\frac{\gamma\;\pi}{ɛ_{0}d}}} > V > \sqrt{\frac{\gamma\;{kd}}{2ɛ_{0}}}} & (1)\end{matrix}$becomes an operation voltage in the present invention.

Dependency of a jetting limit voltage V_(c) with respect to a nozzle ofa certain inside diameter d is shown in the above-mentioned FIG. 19.From this drawing, when a concentration effect of the electric field bythe minute nozzle is considered, the fact that the jetting start voltagedecreases according to the decrease of the nozzle diameter was revealed.

In a case of making a conventional consideration with respect to theelectric field, that is, considering only the electric field which isdefined by a voltage applied to a nozzle and by a distance betweencounter electrodes, as the nozzle becomes smaller, a voltage necessaryfor jetting increases. On the other hand, focusing on local electricfield intensity, due to nozzle miniaturization, it is possible todecrease the jetting voltage.

The jetting according to electrostatic sucking is based on charging ofliquid (liquid solution) at the nozzle edge portion. Speed of thecharging is considered to be approximately around time constantdetermined by dielectric relaxation.

$\begin{matrix}{\tau = \frac{ɛ}{\sigma}} & (2)\end{matrix}$where, ∈: dielectric constant of liquid solution [F/m], and σ: liquidsolution conductivity [S/m]. When it is assumed that dielectric constantof the liquid solution is 10 F/m, and liquid solution conductivity is10⁻⁶ S/m, τ=1.854×10⁻⁶ sec is obtained. Alternatively, when a criticalfrequency is set to f_(c) [Hz],

$\begin{matrix}{f_{c} = \frac{\sigma}{ɛ}} & (14)\end{matrix}$is obtained. It is considered that jetting is impossible because it isnot possible to react to the change of the electric field having fasterfrequency than this f_(c). When estimation regarding the above-mentionedexample is made, the frequency takes around 10 kHz. At this time, in acase of a nozzle radius of 2 μm and a voltage of a little under 500V, itis possible to estimate that current in the nozzle G is 10⁻¹³ m³/s. In acase of the liquid of the above-mentioned example, since it is possibleto perform the jetting at 10 kHz, it is possible to achieve minimumjetting amount at one cycle of around 10 fl (femto liter, 1 fl=10⁻¹⁶ l).

In addition, each of the above-mentioned embodiments, as shown in FIG.20, is characterized by a concentration effect of the electric field atthe nozzle edge portion and by an act of an image force induced to thecounter base plate. Therefore, it is not necessary to have the baseplate or a base plate supporting member electrically conductive asconventionally, or to apply a voltage to these base plate or base platesupporting member. In other words, as the base plate, it is possible touse a glass base plate being electrically insulated, a plastic baseplate such as polyimide, a ceramics base plate, a semiconductor baseplate or the like.

Further, in each of the above-mentioned embodiments, the applyingvoltage to an electrode may be any of plus or minus.

Further, by maintaining a distance between the nozzle and the base platenot more than 500 [μm], it is possible to make the jetting of the liquidsolution easy. Further, preferably, the nozzle is maintained constantwith respect to the base material by doing a feedback control accordingto a nozzle position detection.

Further, the base material may be mounted on a base material holderbeing either electrically conductive or insulated to be maintained.

FIG. 20 shows a side sectional view of a nozzle part of the liquidjetting apparatus as one example of another basic example of the presentinvention. At a side-surface portion of a nozzle 1, an electrode 15 isprovided, and a controlled voltage is applied between the electrode 15and an in-nozzle liquid solution 3. The purpose of this electrode 15 isan electrode for controlling Electrowetting effect. When a sufficientelectric field covers an insulator structuring the nozzle, it isexpected that the Electrowetting effect occurs even without thiselectrode. However, in the present basic example, by doing the controlusing this electrode more actively, a role of a jetting control is alsoachieved. In the case that the nozzle 1 is structured from insulator, anozzle tube at the nozzle edge portion is 1 μm, a nozzle inside diameteris 2 μm and an applying voltage is 300V, it becomes Electrowettingeffect of approximately 30 atmospheres. This pressure is insufficientfor jetting but has a meaning in view of supplying the liquid solutionto the nozzle edge portion, and it is considered that control of jettingis possible by this control electrode.

The above-mentioned FIG. 9 shows dependency of the nozzle diameter ofthe jetting start voltage in the present invention. As the nozzle of theliquid jetting apparatus, one which is shown in FIG. 11 is used. As thenozzle becomes smaller, the jetting start voltage decreases, and thefact that it was possible to perform jetting at a lower voltage thanconventionally was revealed.

In each of the above-mentioned embodiments, conditions for jetting theliquid solution are respective functions of: a distance between nozzleand base material (h); an amplitude of applying voltage (V); and anapplying voltage frequency (f), and it is necessary to satisfy certainconditions respectively as the jetting conditions. Adversely, when anyone of the conditions is not satisfied, it is necessary to changeanother parameter.

This state will be described with reference to FIG. 21.

First, for jetting, a certain critical electric field E_(c) exists,where jetting is not performed unless the electric field is not lessthan the electric field E_(c). This critical electric field is a valuechanged according to the nozzle diameter, a surface tension of theliquid solution, viscosity or the like, and it is difficult to performthe jetting when the value is not more than E_(c). At not less than thecritical electric field E_(c), that is, at jetting capable electricfield intensity, approximately a proportional relation arises betweenthe distance between nozzle and base material (h) and the amplitude ofapplying voltage (V), and when the distance between nozzle and basematerial is shortened, it is possible to make the critical applyingvoltage V smaller.

Adversely, when the distance between nozzle and base material h is madeextremely apart for making the applying voltage V larger, even if thesame electric field intensity is maintained, according to an effect suchas corona discharge or the like, blowout of fluid droplet, that is,burst occurs.

INDUSTRIAL APPLICABILITY

As described above, the present invention is suitable to jet a dropletfor each usage of normal printing as graphic use, printing to specialmedium (film, fabric, steel plate), curved surface printing, and thelike, or patterning coating of wiring, antenna or the like by liquid orpaste conductive material, coating of adhesive, sealer and the like forprocessing use, for biotechnological, medical use, pharmaceuticals (suchas one mixing a plurality of small amount of components), coating ofsample for gene diagnosis or the like.

1. A liquid jetting apparatus to jet a droplet of a charged liquidsolution onto a base material, comprising: a liquid jetting headcomprising a nozzle to jet the droplet from an edge portion, an insidediameter of the edge portion of the nozzle being more than 0.2 μm andbeing not more than 4 μm, and at least the edge portion of the nozzlebeing formed with insulating material, the nozzle being integrallyformed with a nozzle plate; a liquid solution supplying section tosupply the liquid solution into the nozzle; and a jetting voltageapplying section to apply a jetting voltage to the liquid solution inthe nozzle, the jetting voltage applying section comprising a jettingelectrode provided as a layer on a back end surface of the nozzle plate,the jetting electrode having an ink passage hole positioned at a borderbetween the liquid solution supplying section and the inside passage;wherein an inside passage length of the nozzle is set to at least notless than 50 times of the inside diameter of the nozzle at the nozzleedge portion.
 2. The liquid jetting apparatus of claim 1, wherein theinside passage length of the nozzle is set to at least not less than 100times of the inside diameter of the nozzle at the nozzle edge portion.3. The liquid jetting apparatus of claim 1, wherein a wall thickness ofthe nozzle at the nozzle edge portion is set to not more than a lengthequal to the inside diameter of the nozzle at the edge portion of thenozzle.
 4. The liquid jetting apparatus of claim 3, wherein the wallthickness of the nozzle at the edge portion of the nozzle is set to notmore than ¼ of the length equal to the inside diameter of the nozzle atthe nozzle edge portion.
 5. The liquid jetting apparatus of claim 1,wherein at least the edge portion of a surface of the nozzle issubjected to a water repellent processing.
 6. The liquid jettingapparatus of claim 1, wherein an edge surface of the nozzle comprises aninclined surface with respect to a centerline of the in-nozzle passage.7. The liquid jetting apparatus of claim 6, wherein an inclination angleof the edge surface of the nozzle is set to be in a range of 30 to 45degrees (when a state m which a normal line of the inclined surface isparallel to the centerline of the in-nozzle passage is defined as 90degrees).
 8. The liquid jetting apparatus of claim 1, wherein a jettingelectrode of the jetting voltage applying section is provided on a backend portion side of the nozzle.
 9. The liquid jetting apparatus of claim1, wherein the liquid solution supplying section comprises a liquidsolution room, and the ink passage hole is at a border position betweenthe liquid solution room and the inside passage of the nozzle.
 10. Theliquid jetting apparatus of claim 1, wherein the inside diameter of thenozzle at the nozzle edge portion and an inside diameter of the insidepassage of the nozzle are uniform.